Phenylketonuria (PKU) is an inherited metabolic error that results in a toxic build-up of phenylalanine (Phe) in the brain and plasma. Infants are screened at birth to determine if they have the genetic defect responsible for PKU. If an infant is diagnosed with the condition, treatment must be initiated immediately, if there is to be a positive outcome. If PKU is undetected or untreated, the nervous system will suffer severe, irreversible damage and the individual will become severely mentally handicapped. Infants diagnosed with PKU must consume a low phenylalanine diet for life to avoid being affected. The original treatment for this disorder was simply to restrict protein in the diet. This fell far short of what was needed. Berry (1980) found that supplementing the diet with valine, isoleucine and leucine provided a method for improving outcome.
Subsequently, the PKU diets were composed of foods low in protein (and Phe) supplemented with a formula to provide complete nutrition, including amino acids, carbohydrate, fat and essential vitamin and minerals. Because there were no sources of intact protein that did not contain phenylalanine, purified amino acids were provided in lieu of protein (Brown et al 1992, Acosta et al 2002). Purified amino acid diets have an unpleasant taste because many of the free amino acids provide potent gustatory stimulation. In an effort to minimize the off-flavor notes of amino acid diets, Schweikhardt et al (1995) developed a dragee or capsule. Buist and Prince (1995) formulated a less objectionable mixture of amino acids which had less sensory impact.
Compliance is a concern for those with PKU and additional approaches to making palatable and nutritious foods suitable for those with PKU are needed.